I see what you mean now - "remove" is definitely not the correct word to describe the expected operation for this Kata. Thank you for your input.

"people would assume you want move the characters from a string to a different string" - that's precisely the challenge. Extract the n-th string term and return it. You must do so by allocating the characters in a new string. Am I missing something?

Second test case says otherwise:

Assert::That(PythagoreanTriple(5,3,4) , Equals(true));

ok, it's not

vanity

What part specifically?
There are lot of fiddly bits on this one without an objective "best way" to handle it.

Whist has similar rules in Play part

It's a puzzle, the sample tests will walk you through.

it's just a lil faster than the popular solution